In recent years, tissue removal devices have become quite commonplace. Generally, in the field of ocular surgery, tissue removal devices have been found in the form of phacoemulsification devices, as well as ocular cutters. In an ocular cutter, there has generally been found a double needle configuration where an outer chamber or "needle" is concentric with an inner "needle". In the outer needle there is an open port, and the inner needle reciprocates within that open port. Tissue is sucked into the port of the outer needle by vacuum pressure within the inner chamber. When the inner needle reciprocates past the open port, the tissue is sheared. The tissue is then removed down the length of the inner needle by suction.
While these "guillotine" type ocular cutters have been successful instruments, they have posed certain drawbacks. First, there has always been an incentive to provide for the most precise cutting mechanism. The more precise the cutter is, the less chance of tissue trauma. The risk of improper amounts of tissue, or cutting the improper size of the tissue, is also reduced. Frequently, however there is incomplete shear of tissue at the outer needle port.
Second, because the port of the outer needle generally is designed at a distance from the end of the outer needle, present ocular cutters all have a certain minimum width of tissue from the point of contact with the ocular cutter which can not be cut. When cutting takes place, there is always this tolerance which must be taken into account before cutting. Thus, the cutting approach may not be applicable for small, precise cuts which require cutting at the point of contact with healthy ocular tissue.